Calculating Reinforced Cement Concrete (RCC) quantity involves determining both the total volume of the concrete structure or element and the quantities of constituent materials required for that volume.
There are typically two aspects to calculating RCC quantity:
- Calculating the Total Volume of RCC: This determines the overall amount of concrete needed for the structural element (like a beam, column, slab, foundation, etc.) or the entire project.
- Calculating Material Quantities: This involves determining the amounts of cement, fine aggregate (sand), coarse aggregate, water, and steel reinforcement needed for the calculated concrete volume.
Calculating the Total Volume of RCC
The most straightforward way to calculate the total volume of RCC is to determine the geometric volume of the structural element(s).
- For simple shapes: Measure the length, width, and height (or depth) of the element in meters (m). The volume is then calculated as:
- Volume (m³) = Length (m) × Width (m) × Height/Depth (m)
- For complex shapes: Break down the element into simpler geometric shapes, calculate the volume of each part, and sum them up. This is usually done from structural drawings.
For example, a rectangular beam with dimensions 0.2m wide, 0.4m deep, and 5m long would have a volume of 0.2m × 0.4m × 5m = 0.4 m³.
Calculating Material Quantities for a Given Concrete Volume
Once you have the required volume of concrete, you need to calculate the quantities of the raw materials: cement, sand, coarse aggregate, water, and steel reinforcement. The method for calculating concrete ingredients relies on the concrete mix design ratio (e.g., M20 grade often corresponds to a 1:1.5:3 mix approximately).
Concrete Mix Design and Dry Volume
Concrete mix designs specify the ratio of Cement : Fine Aggregate : Coarse Aggregate by volume or weight for a given grade of concrete (e.g., M20, M25).
When cement, sand, and aggregate are mixed with water, they occupy less volume than their dry, loose state due to the filling of voids. To calculate the dry material quantities needed to produce a specific volume of wet concrete, we must account for this reduction in volume. A common practice is to multiply the required wet concrete volume by a factor (typically between 1.52 and 1.57) to get the equivalent volume of dry materials. For example, using a factor of 1.53 as shown in the reference means that 1 m³ of wet concrete requires approximately 1.53 m³ of dry, loose materials.
Calculating Cement, Sand, and Aggregate Quantities
To calculate the volumes of cement, sand, and coarse aggregate for a given volume of wet concrete (let's say 1 m³), use the mix ratio and the dry volume factor.
Let's use the example calculations from the reference, based on a mix ratio of 1:1.5:3 (Cement:Sand:Coarse Aggregate) and a dry volume factor of 1.53:
The total ratio parts are 1 + 1.5 + 3 = 5.5.
-
Cement Quantity:
- Cement Volume = (Ratio of Cement / Sum of Ratios) × Dry Volume Factor × Wet Volume
- Cement Volume = (1 / 5.5) × 1.53 × 1 m³ = 0.278 m³ (as per the reference).
- To get the weight of cement, multiply the volume by the density of cement (approx. 1440 kg/m³): 0.278 m³ × 1440 kg/m³ ≈ 400 kg. Since a standard cement bag is 50 kg, this is about 400 kg / 50 kg/bag = 8 bags.
-
Fine Aggregate (Sand) Quantity:
- Sand Volume = (Ratio of Sand / Sum of Ratios) × Dry Volume Factor × Wet Volume
- Sand Volume = (1.5 / 5.5) × 1.53 × 1 m³ = 0.417 m³ (as per the reference).
-
Coarse Aggregate Quantity:
- Coarse Aggregate Volume = (Ratio of Coarse Aggregate / Sum of Ratios) × Dry Volume Factor × Wet Volume
- Coarse Aggregate Volume = (3 / 5.5) × 1.53 × 1 m³ ≈ 0.835 m³ (completing the calculation based on the reference's method).
Here's a summary for 1 m³ of wet concrete with a 1:1.5:3 mix ratio and a 1.53 dry volume factor:
| Material | Ratio Part | Calculation Formula | Calculated Volume (m³) |
|---|---|---|---|
| Cement | 1 | (1 / 5.5) * 1.53 * 1 m³ | 0.278 |
| Fine Aggregate | 1.5 | (1.5 / 5.5) * 1.53 * 1 m³ | 0.417 |
| Coarse Aggregate | 3 | (3 / 5.5) * 1.53 * 1 m³ | 0.835 |
| Total Dry Volume | 5.5 | Sum of quantities above | 1.53 |
Reference for Cement and Fine Aggregate calculation examples: nischinth.com
Calculating Water Quantity
The amount of water required depends on the water-cement ratio specified by the mix design (typically between 0.4 and 0.6 for RCC).
- Water Weight (kg) = Water-Cement Ratio × Cement Weight (kg)
- For example, if the water-cement ratio is 0.5 and cement weight is 400 kg (for 1 m³ of concrete), Water = 0.5 × 400 kg = 200 kg (or 200 liters, as 1 kg of water ≈ 1 liter).
Calculating Steel Quantity
Calculating steel quantity for RCC is done separately from the concrete mix ingredients. It's based on the structural drawings which show the diameter, shape, and length of each steel bar required.
- Determine total length: Calculate the total length of each diameter of steel bar needed from the bar bending schedule (BBS) or structural drawings.
- Calculate weight: Convert the total length of each diameter into weight using the standard weight per meter formula or pre-calculated values:
- Weight (kg) per meter = (Diameter in mm)² / 162.2
- Total Steel Weight = Sum of (Total Length of bar diameter × Weight per meter of that bar diameter)
Practical Considerations
- Wastage: Always add a percentage (e.g., 5-10%) for wastage of materials, especially aggregate and cement.
- Mix Design Variations: The actual quantities may vary slightly depending on the specific properties of the aggregates and the precise mix design specified by the engineer. Site mix calculations are often approximate; ready-mix concrete suppliers calculate quantities based on their specific designs and material properties.
- Compaction: Ensure calculations are for the final, compacted volume of concrete in the structure.
